The application of fluids to a leather surface is one of the most important operations for the finishing of leather in leather production.
The most common procedures are the spraying of fluid using an air pressure pistol (compressed air jet), the pouring of a thin layer and more recently the so-called pressure procedure using a perforated roll.
All three procedures have advantages and disadvantages.
The spraying procedure using air pressure delivered from rotating nozzles yields the finest layers but it causes a high amount of pollution and results in the highest amount of fluid losses (for example color).
The pouring procedure, which utilizes fluid layers, will cause less pollution, but it can only be applied with special fluids and requires larger application amounts. The pieces of leather must run through at a relatively high speed, which will cause great difficulties when dealing with the synchronization of the drying facility.
The pressure procedure, which uses perforated rolls, will minimize the consumption of fluids (color) and is practicable for a variety of different kinds of fluid and application amounts. Disadvantages of this procedure include the fact that different, relatively expensive application rolls have to be used for the various application amounts. Further, the exchange of rolls is time consuming. The integration of machines with pressure rolls into the drying lane will also cause problems. The running through of leather that is not perfectly smooth will be a problem due to the fact that the leather will crease easily and thus is not possible without a spreading device.